FILE - A customer carries a purchase while exiting a Dick's Sporting Goods Inc. store in Sterling Heights, Michigan, on Aug. 18, 2016. Wednesday, CEO Edward W. Stack announced his company would no longer sell assault-style rifles, high-capacity magazines or guns to people under the age of 21. less

FILE - A customer carries a purchase while exiting a Dick's Sporting Goods Inc. store in Sterling Heights, Michigan, on Aug. 18, 2016. Wednesday, CEO Edward W. Stack announced his company would no longer ... more

Photo: Bloomberg Photo By Sean Proctor

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1. Mass shootings

The AR-15 has been linked to some of the most notorious American shootings in the past few years. It was the weapon of choice for Adam Lanza who killed 20 children and six adults at Sandy Hook Elementary School in 2012. The gun also used at the San Bernardino, Calif. shooting in December.

Omar Mateen killed 49 people Sunday at a gay nightclub Sunday in Orlando. He used a Sig Sauer MCX, similar to an AR-15 but not the same firearm.

Media outlets initially reported Mateen used an AR-15, bringing the firearm back into the public conversation on what type of guns should be available to the public.

Which firearms are considered assault weapons and which are not is hard to distinguish. As the New York Times pointed out in 2013, there is no clear definition of what an assault weapon is. As American’s continue to debate instituting another assault weapon’s ban, the term will have to be more defined.

The AR in AR-15 does not stand for assault rifle. Instead, AR stands for ArmaLite, the company that developed the gun in the 1950s. According to the National Shooting Sports Foundation, the term assault weapon was used by gun control advocates during the 1980s.

Costs for an AR-15 can vary. Impact Guns sells starting around $500. Higher end models can cost more than $2,000.

4. How much does it cost?

Costs for an AR-15 can vary. Impact Guns sells starting around $500. Higher end models can cost more than $2,000.

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5. M16 vs AR-15

The M16 is the military version of the AR-15. The major difference between the two is that the M16 can fire in fully automatic mode, while the AR-15 is only semi-automatic.

5. M16 vs AR-15

The M16 is the military version of the AR-15. The major difference between the two is that the M16 can fire in fully automatic mode, while the AR-15 is only semi-automatic.

Photo: Houston Chronicle

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6. Auto vs. Semi-auto

An automatic weapon is one that will continue to fire until it doesn’t have ammunition. A semi-automatic weapon requires pulling a trigger in order to fire each round, preventing a automatic fire. Automatic weapons are not legal for civilians to own without a permit; semi-automatic weapons are.

The AR-15 can be greatly customized. Cabela’s for example has a whole page dedicated to AR-15 accessories. Scopes, mounts, stocks and magazines are a few of the options to outfit an AR-15.

7. Customization

The AR-15 can be greatly customized. Cabela’s for example has a whole page dedicated to AR-15 accessories. Scopes, mounts, stocks and magazines are a few of the options to outfit an AR-15.

Photo: KAREN BLEIER, AFP/Getty Images

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8. What is it used for?

Outside of defense and competition shooting, AR-15s are big for hunting. They're big for hog hunting but also for shooting prairie dogs, coyotes and deer.

8. What is it used for?

Outside of defense and competition shooting, AR-15s are big for hunting. They're big for hog hunting but also for shooting prairie dogs, coyotes and deer.

Photo: Johnny Hanson, Houston Chronicle

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9. It's popular

It’s America’s most popular firearm, according to the National Rifle Association. The organization says "it’s customizable, adaptable, reliable and accurate" and it can be used in "sport shooting, hunting and self-defense situations." The AR-15’s ability to be modified to your own personal taste is one of the things that makes it so unique.”

The AR-15 was never fully outlawed by the 1994 Assault Weapons Ban. As the website FiveThirtyEight points out, President Bill Clinton’s ban on assault weapons limited the amount of military features that could be put on the firearm.

Users were permitted to having only two of the following options on one firearm: “a folding stock (making the gun slightly easier to conceal), a pistol grip (making the weapon easier to hold and use), a bayonet mount, a flash suppressor (making it harder to see where shots are coming from), or a grenade launcher,” according to FiveThirtyEight. Clinton’s ban lasted from 1994 to 2004.

Stack appeared on Good Morning America on Wednesday morning, two weeks after the mass shooting in Parkland, Fla., which killed 17 people and reinvigorated a national debate over gun control. The alleged shooter, Nikolas Cruz, bought a shotgun from a Dick's store in November 2017, Stack said during the television interview, and though the shotgun was not the weapon used in the massacre, he said his company was moved to act.

"We did everything by the book, and we did everything that the law required, and he was still able to buy a gun," Stack told GMA's George Stephanopoulous.

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